I was hoping that someone had already done this and would be able to give a known answer (that could be entered on the window I captured in my first post.)
Everyone, thank you for the suggestions, but ...
Originally Posted by DNSB
Not absolutely certain but I think you need to attach the line spacing to a <p> or <div> or other lower level tag and not to the body tag. For an .epub file, the line-height in the body will have no effect. If you use the lower level tags, the Kobo UI will not let you modify the line spacing.
Originally Posted by Ripplinger
You can force the Kobo to have tighter line spacing by editing the stylesheet.css file for the epub. 120% or 1.2em works well for me. Once it's within the epub though, the slider to adjust line spacing from the Kobo GUI has no effect, which isn't really a problem if you've set the css correctly to your liking.
Originally Posted by ShellShock
I use Sigil to set the line-height in the stylesheet, usually on the p tag, e.g.,
If there is already a p tag in the stylesheet then you need to add it to that. You can also be more selective--perhaps you do not want to set the line-height for all paragraphs, but only for some styles?
Also, some epubs do not use p tags for paragraphs, they may use divs or spans. This is annoying, but with Sigil you can easily check for this.
Some of these suggestions are as helpful as telling me I can modify the spacing by editing the EPub.
I'm currently using a modified font, so I can get closer line spacing, but I would like to use the internal fonts (once Kobo fixes the italics bug(s).)